Symmetrical coil actuator for a magnetic disk drive

Abstract

An actuator for a magnetic disk drive includes a planar coil which is symmetrical with respect to the center of rotation and has substantially straight active sections extending from the center of rotation on opposite sides of the center of rotation. Four permanent magnets provide a magnetic field. When current is applied to the planar coil, magnetic forces rotate the coil, and an attached actuator arm, about the center of rotation. The symmetrical coil sections eliminate or reduce torsional forces thereby avoiding vibration, improving bearing life and reducing potential servo loop instability.

What is claimed is: 
     
       1. A magnetic disk drive actuator for moving a magnetic head in an arcuate path in read/write relationship with a magnetic disk comprising: an actuator arm rotatable about a center of rotation:   a read/write head mounted on said arm so that said head travels along said arcuate path as said arm is rotated;   a planar coil having only two active sections connected in series and attached to said arm for rotating it about said center of rotation, said planar coil being symmetrical with respect to said center of rotation and having first and second substantially straight active sections extending from one side of said center of rotation and third and fourth substantially straight active sections extending in the same plane on the opposite side of said center of rotation, and symmetrical with said first and second sections having arcuate return traces joining said first and second straight active sections and arcuate return traces joining said third and fourth straight active sections, said active sections and said return traces being connected in series to two connections for supplying current to said coil; and   magnetic means positioned adjacent to each of said active sections of said coil, so that current through said active sections on opposite sides of said center of rotation produces magnetic forces on said coil which act about said center of rotation whereby the rotational forces about the center of rotation are cumulative and the torsional forces cancelled one another avoiding vibration and reducing potential servo loop instability.   
     
     
       2. The actuator recited in claim 1 wherein said magnetic means includes: four permanent magnets respectively positioned adjacent the four active sections of said coil.   
     
     
       3. The actuator recited in claim 2 wherein said magnets have pole faces which are arcuate segments with centers of radii at said center of rotation, said magnets being positioned so that only active traces are adjacent said pole faces as the coil rotates. 
     
     
       4. The actuator recited in claim 1 wherein said arcuate return traces have centers of radii at said center of rotation. 
     
     
       5. The actuator recited in claim 1 wherein said planar coil is a printed circuit coil. 
     
     
       6. The actuator recited in claim 1 further comprising: top and bottom return path members forming a housing for said planar coil and said magnetic means and providing a return path for the magnetic flux of said magnetic means.   
     
     
       7. The actuator recited in claim 6 further comprising: a spindle, said planar coil and said actuator arm being mounted on said spindle, said spindle being mounted for rotation in said bottom return path member.   
     
     
       8. The actuator recited in claim 7 wherein said spindle includes a shaft on which said planar coil and said arm are mounted; a bearing housing concentric with said shaft and having bearings for rotation of said shaft therein; and   a concentric mounting flange for said bearing housing, said mounting flange being mounted in the bottom return path member.   
     
     
       9. The actuator recited in claim 8 wherein said mounting flange is mounted on a datum surface in the base plate of said magnetic disk drive.